This invention relates to an acicular electroconductive titanium oxide having on the surface an electroconductive layer comprising tin oxide and antimony oxide and a process for producing it. Acicular electroconductive titanium oxide is useful as electrical conductivity-imparting agent or antistatic agent for plastics, rubbers, fibers, etc. and electrical conductivity-imparting agent for support of recording materials such as electrophotographic copying paper and electrostatic recording paper.
As electrical conductivity-imparting agents, there have been known antimony-containing tin oxide powder, conductive powder comprising titanium dioxide powder having on its surface an electroconductive layer comprising tin oxide or tin oxide and antimony oxide and the like (U.S. Pat. Nos. 4,373,013 and 4,452,830). Recently, an electroconductive material mainly composed of fibrous potassium titanate coated on the surface with tin oxide has been proposed in Japanese Patent Examined Publication (Kokoku) No. 26933/86.
Generally speaking, electrical conductivity-imparting agents of an acicular form (including fibrous form), as compared with spherical form, and furthermore the agents which are lower in their powder resistivity, namely, higher in electrical conductivity, can give resin articles and rubber articles of the desired conductivity even with the addition thereof in a small amount to the article. Commercially available antimony-containing tin oxide powder and electroconductive powder comprising titanium dioxide having on the surface an electroconductive layer comprising tin oxide and antimony oxide have its own powder resistivity of 1-10 .OMEGA.cm which shows very excellent electrical conductivity, but since they are in the form of spherical powder, they must be added in an amount of more than 50% to the media such as resin and rubber in order to impart the desired conductivity to the media. Addition of them in such a large amount causes reduction in strength of articles such as electroconductive resins and electroconductive rubbers and besides it is not economical.
As an approach to solve these problems, there has been recently proposed, for example, a white conductive material comprising fibrous potassium titanate coated on its surface with an electroconductive layer of tin oxide. This is satisfactory on the point of shape, but is high in powder resistivity and poor in strength and, therefore, the material is still not satisfactory in this respect. Even if the composition of the electroconductive layer is changed to that of tin oxide and antimony oxide, powder resistivity obtained is at most about 50-100 .OMEGA.cm due to the influence of potassium component.
Noticing the superiority of acicular electroconductive materials as electrical conductivity imparting agent, the inventors have attempted to coat the surface of acicular titanium oxide as a substrate material with an electroconductive layer. As a result, the following have been found and this invention has been accomplished. (a) The known acicular titanium oxide obtained by conventional methods inevitably contains impurities such as alkali metals, alkaline earth metals and phosphorus compounds which come from starting materials and which cannot be removed by such means as water leaching. (b) When an electroconductive layer is coated on the titanium oxide in which the impurities remain in more than a specific amount, formation of the coating layer on the surface of titanium oxide is difficult or even if the electroconductive layer can be formed, good conductivity cannot be obtained. (c) These impurities can be removed by acid treatment and/or alkali treatment.